Field of the Invention
The present disclosure relates to a liquid discharge head mounted on a liquid discharge apparatus, and more particularly, to a liquid discharge head having a function of preventing destruction caused by an electrostatic surge.
Description of the Related Art
In a liquid discharge apparatus that discharges liquid onto a recording medium to perform recording, a liquid discharge head including a discharge port for discharging liquid is provided The liquid discharge head is provided with energy generating elements for generating energy for discharging liquid, and each of the energy generating elements includes a heating resistance element or a piezoelectric element driven by an electric signal, for example. The energy generating elements are integrated on a recording element substrate including a semiconductor substrate, and a wiring line electrically connected to each of the energy generating elements is also formed on the recording element substrate. The recording element substrate may be provided with a driving circuit for driving each of the energy generating elements according to record data supplied from the liquid discharge apparatus.
In the liquid discharge head, the energy generating elements and other circuit elements may be destroyed caused by electrostatic discharge, which is a problem. As a measure against such electrostatic breakdown, Japanese Patent Application Laid-Open No. 2013-184420 discusses providing a functional element for regulating voltage to a predetermined value or less between a power source wiring line and another wiring line (e.g., a grounding wiring line) having a large electric capacitance in a contact substrate in a liquid discharge head. The contact substrate is provided in the liquid discharge head to receive each signal used for driving from a main body of a liquid discharge apparatus, and is connected to a recording element substrate via a wiring member. When the functional element is provided, even if a high-voltage electrostatic surge is applied to the power source wiring line, a surge current can be released to the wiring line having a large electrical capacitance, so that the power source wiring line in the recording element substrate can be protected. The electrical capacitance means a capability to electrostatically store a charge as an isolated conductor. The measure discussed in Japanese Patent Application Laid-Open No. 2013-184420 is more effective for a wiring line at a stable potential such as a power source wiring line for driving an energy generating element or a power source wiring line to a driving circuit.
This measure is effective for a case where the surge current from the power source wiring line is released to a wiring line at a reference potential having a large parasitic capacitance.
The measure discussed in Japanese Patent Application Laid-Open No. 2013-184420 is to connect the functional element between the power source wiring line at a relatively stable potential and, for example, the grounding wiring line, and implements protection when an electrostatic surge is applied to the power source wiring line. However, in this measure, when an electrostatic surge having a higher voltage is applied to a signal wiring line used for driving, the energy generating element and the driving circuit may be damaged. When the functional element for releasing an electrostatic surge is connected to a wiring line, a parasitic capacitance of the wiring line increases, so that a signal to be propagated on the wiring line is delayed. Thus, a functional element for protection from an electrostatic surge cannot be connected to a signal wiring line requiring high responsiveness.